Study on the efficacy and mechanism of Fe-TiO2 visible heterogeneous Fenton catalytic degradation of atrazine

Strong metal-support interaction (SMSI) in environmental catalysis: Mechanisms, application, regulation strategies, and breakthroughs

The strong metal-support interaction (SMSI) in supported catalysts plays a dominant role in catalytic degradation, upgrading, and remanufacturing of environmental pollutants. Previous studies have shown that SMSI is crucial in supported catalysts' activity and stability. However, for redox reactions catalyzed in environmental catalysis, the enhancement mechanism of SMSI-induced oxygen vacancy and electron transfer needs to be clarified. Additionally, the precise control of SMSI interface sites remains to be fully understood. Here we provide a systematic review of SMSI's catalytic mechanisms and control strategies in purifying gaseous pollutants, treating organic wastewater, and valorizing biomass solid waste. We explore the adsorption and activation mechanisms of SMSI in redox reactions by examining interfacial electron transfer, interfacial oxygen vacancy, and interfacial acidic sites. Furthermore, we develop a precise regulation strategy of SMSI from systematical perspectives of interface effect, crystal facet effect, size effect, guest ion doping, and modification effect. Importantly, we point out the drawbacks and breakthrough directions for SMSI regulation in environmental catalysis, including partial encapsulation strategy, size optimization strategy, interface oxygen vacancy strategy, and multi-component strategy. This review article provides the potential applications of SMSI and offers guidance for its controlled regulation in environmental catalysis.

Atrazine degradation through a heterogeneous dual-effect process using Fe-TiO2-allophane catalysts under sunlight

This study investigated the novel application of Fe-TiO2-allophane catalysts with 6.0 % w/w of iron oxide and two TiO2 proportions (10 % and 30 % w/w) for degrading atrazine (ATZ) using the heterogeneous dual-effect (HDE) process under sunlight. Comparative analyses with Fe-allophane and TiO2-allophane catalysts were conducted in both photocatalysis (PC) and HDE processes. FTIR spectra reveal the unique hydrous feldspathoids structure of allophane, showing evidence of new bond formation between Si-O groups of allophane clays and iron hydroxyl species, as well as Si-O-Ti bonds that intensified with higher TiO2 content. The catalysts exhibited an anatase structure. In Fe-TiO2-allophane catalysts, iron oxide was incorporated through the substitution of Ti4+ by Fe3+ in the anatase crystal lattice and precipitation on the surface of allophane clays, forming small iron oxide particles. Allophane clays reduced the agglomeration and particle size of TiO2, resulting in an enhanced specific surface area and pore volume for all catalysts. Iron oxide incorporation decreased the band gap, broadening the photoresponse to visible light. In the PC process, TiO2-allophane achieves 90 % ATZ degradation, attributed to radical species from the UV component of sunlight. In the HDE process, Fe-TiO2-allophane catalysts exhibit synergistic effects, particularly with 30 % w/w TiO2, achieving 100 % ATZ degradation and 85 % COD removal, with shorter reaction time as TiO2 percentage increased. The HDE process was performed under less acidic conditions, achieving complete ATZ degradation after 6 h without iron leaching. Consequently, Fe-TiO2-allophane catalysts are proposed as a promising alternative for degrading emerging pollutants under environmentally friendly conditions.

Iron-doped bismuth oxybromides as visible-light-responsive Fenton catalysts for the degradation of atrazine in aqueous phases

Pesticides and its degradation products, being well-known residues in soil, have recently been detected in many water bodies as pollutants of emerging concerns, and thus there is a contemporary demand to develop viable and cost-effective techniques for the removal of related organic pollutants in aqueous phases. Herein, a visible-light-responsive Fenton system was constructed with iron-doped bismuth oxybromides (Fe-BiOBr) as the catalysts. Taking the advantage of sustainable Fe(III)/Fe(II) conversion and optimized H2O2 utilization, the optimal Fe-BiOBr-2 catalyst showed an excellent atrazine removal efficiency of 97.61% in 120 min, which is superior than the traditional homogeneous Fenton and the majority of heterogeneous processes documented in the literature. In this photo-Fenton system, hydroxyl (·OH) and superoxide (·O2-) radicals were dominant active species contributed to the oxidative degradation of atrazine. Due to the production of various active radicals, five degradation pathways were proposed based on the identification of intermediates and degradation products. Overall, this work not only demonstrates a fundamental insight into creating highly efficient and atom economic photo-Fenton systems, but also provides a complementary strategy for the treatment of organic pollutants in water.

Performance and mechanism investigation on the enhanced photocatalytic removal of atrazine on S-doped g-C3N4

Developing efficient method for removing low-concentration atrazine, a poisonous chlorinated triazine herbicide with poor biodegradability, was an important measure to control its risk. In this work, highly efficient photocatalytic oxidation of atrazine was achieved on S-doped g-C3N4 (S-g-C3N4). Approximate 99.6% of atrazine was removed in 2 h with a reaction rate constant of 2.76 h-1, nearly 2.44 times that on g-C3N4. The mechanism investigation indicated the improved photocatalytic performance of S-g-C3N4 could be attributed to the enlarged specific surface area, extended light absorption as well as the accelerated separation of the photogenerated charge carriers, which was brought about by the successful doping of sulfur in g-C3N4. Meanwhile, the influence of sulfur doping on the generation and contribution of different reactive species in atrazine removal were also elucidated. It revealed that compared with g-C3N4, the more positive valence band potential of S-g-C3N4 was beneficial to produce more singlet oxygen, which could react synergistically with the superoxide radicals, leading to the improved atrazine removal efficiency. The S-g-C3N4 based photocatalytic system also showed preferential photocatalytic oxidation capability in removing other triazine pesticides compared with 3-chlorophenol (3-CP). The potential applicability of the S-g-C3N4 based photocatalytic system in removing atrazine in high salty water was also investigated, which exhibited superior anti-interference ability towards virous coexistent ions. This work will provide essential and fundamental information for establishing efficient photocatalytic system for triazine type pollutants in waters.

Removal of organic pollutants through hydroxyl radical-based advanced oxidation processes

The use of Advance Oxidation Process (AOPs) has been extensively examined in order to eradicate organic pollutants. This review assesses the efficacy of photolysis, O3 based (O3/UV, O3/H2O2, O3/H2O2/UV, H2O2/UV, Fenton, Fenton-like, hetero-system) and sonochemical and electro-oxidative AOPs in this regard. The main purpose of this review and some suggestions for the advancement of AOPs is to facilitate the elimination of toxic organic pollutants. Initially proposed for the purification of drinking water in 1980, AOPs have since been employed for various wastewater treatments. AOPs technologies are essentially a process intensification through the use of hybrid methods for wastewater treatment, which generate large amounts of hydroxyl (•OH) and sulfate (SO4·-) radicals, the ultimate oxidants for the remediation of organic pollutants. This review covers the use of AOPs and ozone or UV treatment in combination to create a powerful method of wastewater treatment. This novel approach has been demonstrated to be highly effective, with the acceleration of the oxidation process through Fenton reaction and photocatalytic oxidation technologies. It is clear that Advance Oxidation Process are a helpful for the degradation of organic toxic compounds. Additionally, other processes such as •OH and SO4·- radical-based oxidation may also arise during AOPs treatment and contribute to the reduction of target organic pollutants. This review summarizes the current development of AOPs treatment of wastewater organic pollutants.

Efficient photoelectrocatalytic degradation of amoxicillin using nano-TiO2 photoanode thin films: A comparative study with photocatalytic and electrocatalytic methods

Excessive utilization of antibiotics in human, animal, and aquaculture poses a substantial threat to human health and the environment. Photoelectrochemical processes are increasingly applied for water remediation because they generate oxidizing species and mineralize organic pollutants, making even small water quantities more amenable for utilization. Thus, this study presents the fabrication of an efficient nano-TiO2 photoanode thin film (PATF) specifically designed for the photoelectrocatalytic (PEC) degradation of amoxicillin (AMX). The TiO2 PATFs were deposited on fluorine-doped tin oxide (FTO) substrate using an ultrasonic spray pyrolysis process with various titanium isopropoxide (TTIP) acetylacetone (AcacH) molar ratios (1:1 to 1:10). The PEC oxidation of AMX was investigated using various molar ratios of TTIP:AcacH TiO2 PATF/FTO by linear sweep voltammetry, and a 1:8 M ratio of PATF exhibited superior PEC oxidation activity than other TiO2 PATFs. Subsequently, the PEC degradation efficiency of AMX was compared with that of photocatalytic (PC) and electrocatalytic (EC) methods. The results demonstrated that the PEC process effectively eliminated 76.2% of AMX within 120 min at 0.8 V, outperforming the removal rates attained by the EC (32.3%) and PC (52.6%). Notably, increasing the voltage to 1.0 V accelerated the PEC degradation of AMX, attaining a removal efficiency of 91.2% within 90 min and exceeding 95% within 120 min.

Potential use of foundry sand and furnace blast sand for fabrication of visibly active composite to promote circular economy/waste management for treating real agro-industrial wastewater

A two-step process of coagulation/flocculation followed by a simultaneous dual process (photocatalysis + photo-Fenton) is developed to treat real pulp and paper (P and P) industry wastewater. The rigid stout color wastewater was treated using a sunlight-responsive and cost-effective Fe-TiO₂ composite using recirculating photoreactor with a total working volume of 4 L. The key point of this study is that the treatment is done in very less time (90 min), and it incorporates the idea of circular economy, as the composite is fabricated out of industrial rejects. The further intensification of the process was done by proper process optimization of both approaches. With an initial concentration of stout color (0.78 AU) and chemical oxygen demand (COD) (2200 mg/L), the optimized conditions gave a good reduction in % color and % COD, that is, 64.1% and 41.8% (1280 mg/L) after coagulation/flocculation and 89.74% and 53.12% (600 mg/L) after dual, respectively. The composite was characterized by using various techniques like field emission scanning electron microscopy (FESEM)/energy dispersive X-ray analysis (EDAX), UV-visible diffuse reflectance spectroscopy (UV-vis DRS), and X-ray diffraction (XRD) to check the catalyst composition, complexes formed between Fe-TiO₂ , and the catalyst intactness in both fresh and 50 times recycled composite. A trapping study was also performed using various quenchers to confirm that OH^• plays a major role in the present study among other radicals produced where 55-60% drop in color removal was seen. In order to foresee the commercial use of this study, the process' cost was also estimated. PRACTITIONER POINTS: Industrial waste products were used to fabricate inert support that promoted the idea of circular economy/waste management. Iron from the waste used to execute photo-Fenton process along with forming Fe-TiO₂ complex to make it visibly active composite. Enhanced production of OH radicals facilitated removal of stout color and COD from the real pulp and paper industry wastewater in just 90 min. Coagulation/flocculation followed by dual technique proved to be the best approach out of three different approaches applied. Composite showed excellent durability even after 50 recycles.

Real-Time Monitoring of the Atrazine Degradation by Liquid Chromatography and High-Resolution Mass Spectrometry: Effect of Fenton Process and Ultrasound Treatment

High resolution mass spectrometry (HRMS) was coupled with ultra-high-performance liquid chromatography (uHPLC) to monitor atrazine (ATZ) degradation process of Fenton/ultrasound (US) treatment in real time. Samples were automatically taken through a peristaltic pump, and then analysed by HPLC-HRMS. The injection in the mass spectrometer was performed every 4 min for 2 h. ATZ and its degradation metabolites were sampled and identified. Online Fenton experiments in different equivalents of Fenton reagents, online US experiments with/without Fe²⁺ and offline Fenton experiments were conducted. Higher equivalents of Fenton reagents promoted the degradation rate of ATZ and the generation of the late-products such as Ammeline (AM). Besides, adding Fe²⁺ accelerated ATZ degradation in US treatment. In offline Fenton, the degradation rate of ATZ was higher than that of online Fenton, suggesting the offline samples were still reacting in the vial. The online analysis precisely controls the effect of reagents over time through automatic sampling and rapid detection, which greatly improves the measurement accuracy. The experimental set up proposed here both prevents the degradation of potentially unstable metabolites and provides a good way to track each metabolite.

Detection of radicals produced during electro-oxidation of atrazine using commercial DSA®-Cl2 in methanol media: Keys to understand the process

This work reports the radicals detected and identified during the degradation of atrazine in methanol medium in the presence and absence of different proportions of water (0%, 5%, and 10%). The determination of these radicals is an important step to understand the electrolysis processes in methanol medium and contribute to clarify the degradation mechanism. Furthermore, the parameters for the successful removal of the contaminant were optimized and the results showed that the application of the technique led to the removal of nearly 99.8% of atrazine after 1 h of electrolysis. The oxidation kinetics was found to be very fast and most of the atrazine molecule in the medium was degraded in the first hour of electrolysis. The results obtained from a thorough analysis conducted with a view to evaluating the effects of different current densities and initial pH values on atrazine degradation showed that the application of higher current densities resulted in lower energy consumption, as this led to faster removal of atrazine. Additionally, the initial pH of the solution was found to favor the formation of different species of active chlorine. The radicals formed during the electro-oxidation process were detected by electron paramagnetic resonance spectroscopy and include hydroxyl, methoxy and hydroxymethyl. The use of methanol for the degradation of pollutants is a highly promising technique and this work shows that the identification of the different radicals formed in the process can be the key to understanding the degradation mechanism.

Toxicological effects, environmental behaviors and remediation technologies of herbicide atrazine in soil and sediment: A comprehensive review

Atrazine has become one of the most popular applied triazine herbicides in the world due to its high herbicidal efficiency and low price. With its large-dosage and long-term use on a global scale, atrazine can cause widespread and persistent contamination of soil and sediment. This review systematically evaluates the toxicological effects, environmental risks, environmental behaviors (adsorption, transport and transformation, and bioaccumulation) of atrazine, and the remediation technologies of atrazine-contaminated soil and sediment. For the adsorption behavior of atrazine on soil and sediment, the organic matter content plays an extremely important role in the adsorption process. Various models and equations such as the multi-media fugacity model and solute transport model are used to analyze the migration and transformation process of atrazine in soil and sediment. It is worth noting that certain transformation products of atrazine in the environment even have stronger toxicity and mobility than its parent. Among various remediation technologies, the combination of microbial remediation and phytoremediation for atrazine-contaminated soil and sediment has wide application prospects. Although other remediation technologies such as advanced oxidation processes (AOPs) can also efficiently remove atrazine from soil, some potential problems still need to be further clarified. Finally, some related challenges and prospects are proposed.

Degradation of Residual Herbicide Atrazine in Agri-Food and Washing Water

Atrazine, an herbicide used to control grassy and broadleaf weed, has become an essential part of agricultural crop protection tools. It is widely sprayed on corn, sorghum and sugar cane, with the attendant problems of its residues in agri-food and washing water. If ingested into humans, this residual atrazine can cause reproductive harm, developmental toxicity and carcinogenicity. It is therefore important to find clean and economical degradation processes for atrazine. In recent years, many physical, chemical and biological methods have been proposed to remove atrazine from the aquatic environment. This review introduces the research works of atrazine degradation in aqueous solutions by method classification. These methods are then compared by their advantages, disadvantages, and different degradation pathways of atrazine. Moreover, the existing toxicological experimental data for atrazine and its metabolites are summarized. Finally, the review concludes with directions for future research and major challenges to be addressed.

Recent Advances in Endocrine Disrupting Compounds Degradation through Metal Oxide-Based Nanomaterials

Endocrine Disrupting Compounds (EDCs) comprise a class of natural or synthetic molecules and groups of substances which are considered as emerging contaminants due to their toxicity and danger for the ecosystems, including human health. Nowadays, the presence of EDCs in water and wastewater has become a global problem, which is challenging the scientific community to address the development and application of effective strategies for their removal from the environment. Particularly, catalytic and photocatalytic degradation processes employing nanostructured materials based on metal oxides, mainly acting through the generation of reactive oxygen species, are widely explored to eradicate EDCs from water. In this review, we report the recent advances described by the major publications in recent years and focused on the degradation processes of several classes of EDCs, such as plastic components and additives, agricultural chemicals, pharmaceuticals, and personal care products, which were realized by using novel metal oxide-based nanomaterials. A variety of doped, hybrid, composite and heterostructured semiconductors were reported, whose performances are influenced by their chemical, structural as well as morphological features. Along with photocatalysis, alternative heterogeneous advanced oxidation processes are in development, and their combination may be a promising way toward industrial scale application.

Intermediate accumulation and toxicity reduction during the selective photoelectrochemical process of atrazine in complex water bodies

Selective removal of atrazine (ATZ) in wastewater and clarification of the degradation intermediate-toxicity correlation are of great importance. A newly molecularly imprinted, {001} facets-exposed TiO₂ (MI-TiO_2,001) photoanode with strong catalytic and selective ability was designed. ATZ was selectively removed from pesticide wastewater, reaching 1.9 µg L^-1, approximately 1/10 of the concentration achieved with nonselective treatment. This selective removal originated from the preferential adsorption and enrichment of ATZ onto MI-TiO_2,001. The highly specific recognition relied on the halogen bond and strong hydrogen bond formed between the Cl atom and triazine ring π orbital of ATZ and the surface -OH group of MI-TiO_2,001 as well as the recognition of MI-TiO_2,001 to the shape and size of ATZ. The specific interaction leads to different accumulations of intermediates. The correlation of intermediate and toxicity was also discussed. Aquatic toxicity was rapidly reduced through the direct dealkylation path, and due to the accumulation of highly toxic 2‑hydroxy-4-ethylamino-6-isopropylamino-s-triazine, there will be transient fluctuations via the dechlorination-hydroxylation path first. The final product was identified as nearly nontoxic cyanuric acid, the selective accumulation of which indicated that there was almost 100% removal of aquatic toxicity and cytotoxicity with only 9.8% removal of total organic carbon. This work provides new insight into the correlation of pollutant degradation intermediates and changes in toxicity.

Effects of Atrazine on Chernozem Microbial Communities Evaluated by Traditional Detection and Modern Sequencing Technology

Atrazine is a long residual herbicide commonly used in maize fields. Although atrazine can effectively control weeds and improve crop yield, long-term application leads to continuous pollution in the agricultural ecological environment, especially in the soil ecosystem, and its impact on soil microorganisms is still not clear. Four methods were used in the experiment to clarify the effect of atrazine on the bacterial populations of cultivated soil layers of chernozem in a cold region in different periods: high-performance liquid chromatography (HPLC), colorimetry, microplate, and high-throughput sequencing. The level of residual atrazine in cold chernozem decreased from 4.645 to 0.077 mg/kg soil over time, and the residue gradually leached into deep soil and then decreased after accumulating to a maximum value. Atrazine significantly affected the activities of urease and polyphenol oxidase activity in the soil layers at different periods but had no significant effect on sucrase and phosphatase activity. Atrazine significantly reduced the diversity of microbial carbon source utilization and total activity in soil layers of 0-10 and 20-30 cm but only reduced the diversity of microbial carbon source utilization in the 10-20 cm layer. Atrazine had no significant effect on bacterial populations (10-12 phyla, 29-34 genera), but had a slight effect on the relative abundance of various groups. Atrazine significantly reduced the diversity of bacterial populations in cultivated soil layers of chernozem in a cold region, and the diversity of bacterial populations decreased with decreased residue. This lays a foundation for guiding the safe use of herbicides on farmland in Northeast China.

Photocatalytic activity of G-TiO2@Fe3O4 with persulfate for degradation of alizarin red S under visible light

A composite photocatalyst combined with TiO₂, graphite (G) and Fe₃O₄ was prepared by co-precipitation method. Then the G-TiO₂@Fe₃O₄ was employed with persulfate (PS) to degrade alizarin red S (ARS) under visible light. The removal rate of ARS reached 100% after 60 min irradiation. The degradation rate constant of G-TiO₂@Fe₃O₄/PS exhibited 20.8, 9.0 and 3.1 times than that of TiO₂, G-TiO₂ and G-TiO₂@Fe₃O₄, respectively. The effects of photocatalyst dosage, mass ratios of graphite and Fe₃O₄ to TiO₂, PS dosage, initial pH and ARS concentration on the degradation efficiency were investigated. The optimal removal efficiency of ARS was obtained when G-TiO₂@Fe₃O₄ dosage was 0.25 g/L, G: TiO₂ = 0.005, Fe₃O₄: TiO₂ = 0.8, PS concentration was 6 mmol/L, initial pH = 3, and initial concentration of ARS was 100 mg/L. The SO₄·^- was demonstrated more important than O₂^- and·OH in the degradation of ARS. The intermediates and possible degradation pathways of ARS were discussed. Reuse and stability of G-TiO₂@Fe₃O₄ were also tested, and 88.3% photocatalytic activity was maintained after five cycles. Therefore, the proposed G-TiO₂@Fe₃O₄/PS not only had excellent photocatalytic activity, but also showed superior stability and reusability.